The closest prior art of which the applicant is aware is disclosed in U.S. Pat. No. 2,989,316 to R. D. Perry et al., U.S. Pat. No. 3,750,452 to Frank, U.S. Pat. No. 1,934,652 to G. A. Anderson, Japanese Patent No. 5-337587 to Takeda, U.S. Pat. No. 4,243,237, U.S. Pat. No. 4,362,306, and U.S. Pat. No. 4,771,933 (all to Rohm).
With reference to the Takeda reference, it disclosed a method that is used to expand the upper portion (1b) of a tube (1) radially outward as shown in FIG. 1. However, the inner diameter of the upper portion (1b) is greater than that of the tube (1), which means that the wall thickness of the upper portion (1b) is reduced as shown in FIG. 1. In such a manner, when the reduced upper portion (1b) of the tube (1) is connected to a high pressure connector, the reduced upper portion (1b) cannot entirely withstand the high pressure and pulse exerted by the high pressure connector, thereby easily breaking the tube (1) at the reduced upper portion (1b).
With reference to the Anderson reference, it disclosed a method for extruding a slug (1) made of a suitable metal such as aluminum into a cop tube (13). A punch (10) is forced downward to enter the bore (2) of the slug (1). Pressure on the punch (10) will result in an extrusion of the metal of the slug (1) downward through the bore (5), and hence away from the punch (10), resulting in the production of a tubular cylinder (13). As the tube (13) is extruded, it will depress the plunger (7) against the tension of the spring (9) and this die operation is continued until only a sufficient metal is left in the bore (12) to form a head (14) on the tube (13). When the punch is retracted, the pressure of the coiled spring (9) will then force the tube (13) upward, thereby ejecting it from the die (3). The cop tube (13) as thus formed is clearly illustrated in FIG. 4 (column 2, lines 25-55). Accordingly, the slug (1) with a short length as shown in FIG. 2 is continuously extruded to be elongated into the cop tube (13) as shown in FIGS. 3 and 4, finally leaving the head (14) on the cop tube (13). In such a manner, such a method is only suitable for extruding a soft metal such as aluminum, copper, lead and the like, and cannot be used to machine a solid metal. When the head (14) of the tube (13) is connected to a high pressure connector, it cannot entirely withstand the high pressure and impact exerted by the high pressure connector, thereby easily breaking the tube (13) at the head (14).
With reference to the R. D. Perry et al. reference, it disclosed a chuck or collet (36) which has a fixed diameter such that it is used to clamp workpieces of the same diameter only, and cannot be used to clamp workpieces of different diameters, thereby greatly limiting the versatility of the chuck (36) such that the chuck (36) has to be replaced when the intent is to machine workpieces of different diameters, thereby causing inconvenience to an operator.
With reference to the Frank reference, it disclosed a collet assembly (20) including a circular array of rigid segments or jaws (23) having outer tapered surfaces complementary to the surface of the tapered bore (21) of the die ring (19) (column 3, lines 5-10). However, when a workpiece is gripped in the jaws (23) of the collet assembly (20) to be machined by a lathe, it is difficult to machine the workpiece by turning-machining operation, thereby causing inconvenience to the operator. In addition, the workpiece is clamped between the cone-shaped walls of the jaws (23) such that the workpiece has to be deeply inserted into the jaws (23) of the collet assembly (20) so as to provide a secure grip to position the workpiece in place. In such a manner, the surface of the workpiece to be machined is decreased. Further, the jaws (23) of the collet assembly (20) are used to clamp workpieces of smaller diameters only, and cannot be used to securely clamp workpieces of larger diameters, thereby greatly limiting the versatility of the collet assembly (20) such that the jaws (23) of the collet assembly (20) have to be replaced when the intent is to machine workpieces of larger diameters, thereby causing inconvenience to the operator.
Both of the Perry et al. and Frank references use an inclined plane to press a workpiece so as to clamp the workpiece in place. However, it is necessary to exert a great force so as to clamp the workpiece, thereby causing inconvenience to the user. In addition, the workpiece has a great length to be deeply inserted into the collet assembly to facilitate the inclined plane securely clipping the workpiece, thereby reducing the area of the working surface of the workpiece to be machined.
A conventional method in accordance with the prior art shown in FIGS. 13-15 is used for forming a connecting pipe (50) of a high pressure connector (5) for fluid which includes an upper sleeve (54) fitted on an annular shoulder (51) of the connecting pipe (50), a lower sleeve (55) securely fitted on the connecting pipe (50), and a hose (56) clamped between a plurality of teeth (53) of the connecting pipe (50) and the lower sleeve (55). The method comprises providing a tubular workpiece (not shown); performing a first turning-machining operation on the upper portion of the workpiece so as to form the annular shoulder (51); performing a second turning-machining operation on the upper portion of the workpiece so as to form a tapered hole (52) in the workpiece; performing a third turning-machining operation on the lower portion of the workpiece so as to form a plurality of teeth (53); and finally performing a fine turning-machining operation on the workpiece so as to finish the teeth (53). By such a process, the outer diameter of the teeth (53) is significantly smaller than that of the annular shoulder (51) such that it is necessary to remove the surface material of the workpiece during the turning-machining operations which is time consuming, thereby causing waste in time and cost. In addition, the teeth (53) are formed by means of turning-machining rather than forging and so have a low strength such that the inner wall (58) of the connecting pipe (50) located adjacent to the teeth (53) is easily deformed due to a high pressure. The present invention has arisen to mitigate and/or obviate the disadvantage of the conventional method for forming a connecting pipe of a high pressure connector.